Segment Information - Assets By Reportable Segment (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total segment assets	$ 18,219	$ 18,718
Operating Segments
Segment Reporting Information [Line Items]
Total segment assets	15,687	15,321
Engineered Products and Solutions
Segment Reporting Information [Line Items]
Total segment assets	10,447	10,325
Global Rolled Products
Segment Reporting Information [Line Items]
Total segment assets	4,153	3,955
Transportation and Construction Solutions
Segment Reporting Information [Line Items]
Total segment assets	$ 1,087	$ 1,041